This invention relates to a fuel injector for use in delivering fuel under high pressure to a combustion space of an engine. The invention relates, in particular, to an injector of the type having a plurality of axially spaced outlet openings or rows of outlet openings and means for controlling the number of openings or rows of outlet openings through which fuel is to be delivered.
FIG. 1 illustrates part of a known fuel injector which includes an outer valve needle 1 which is guided for sliding movement within a blind bore 2 provided in a nozzle body 3. The bore 2 defines a seating with which the needle 1 is engageable to control the fuel supply to a first outlet opening 4. Although only a single opening 4 is illustrated, a row of such openings may be provided, the openings being located at the same axial position relative to the bore 2.
The needle 1 is provided with the blind bore 5 within which an inner needle 6 is reciprocable. The inner end of the inner needle 6 is of enlarged diameter and is engageable with a step or shoulder defined by the inner end of a tubular sleeve 7 located within the bore 5. The sleeve 7 is arranged such that, once the outer needle 1 has moved away from the seating by a predetermined distance, further movement is transmitted to the inner needle 6 to lift the inner needle 6 away from the seating and allow fuel delivery through a second outlet opening 8 or group of such openings. A suitable control arrangement is provided to control the distance through which the outer needle 1 moves, in use.
It will be appreciated that by appropriately controlling the injector, fuel can be delivered either through the first opening or openings 4 alone or through both the first and second openings 4, 8. It is desirable to provide a fuel injector in which, in all modes of operation, the injector operates as if fuel is being delivered through a single outlet opening or row of openings. Clearly, in the known arrangement this is not achieved as, in one mode of operation, fuel delivery is occurring through two openings or groups of openings.
By way of background to the present invention, U.S. Pat. No. 5,540,200 describes a fuel injection valve for a gasoline engine in which the fuel sprays from different openings provided in a nozzle body are collided to cause atomisation of the fuel as a result of a resonance phenomenon.
According to the present invention there is provided a fuel injector comprising a nozzle body, a first outlet opening, a second outlet opening, and means for controlling fuel delivery through the first and second outlet openings, wherein the axes of the first and second outlet openings intersect one another downstream of the outlet openings. The axes of the first and second outlet openings are arranged such that, when fuel is delivered through both the first and second outlet openings, a combined spray formation is formed which is substantially equivalent to a single spray formation having been delivered from a single opening. The means for controlling fuel delivery through the first and second outlet openings are arranged to permit fuel delivery from only one of the outlet openings.
The fuel injector permits the fuel mass flow and the fuel momentum mass flow into a single spray to be varied by merging the fuel sprays from both the first and second outlet openings, with each of the first and second outlet openings normally adopting a fully open or fully closed state. This avoids the undesireable spray formation which can occur in other designs of variable area nozzle injectors where the amount by which an outlet opening is uncovered is used to vary the fuel flow into each fuel spray formation.
By arranging for the axes of the openings to intersect, when fuel is delivered through both outlet openings at the same time the sprays impinge upon and interfere with one another to form a single combined spray formation. Injection of a combined spray formation into the combustion chamber of the associated engine improves engine emissions and combustion noise performance.
Preferably, the first and second outlet openings are arranged so as to give rise to a combined spray formation which is substantially equivalent to a single spray formation having been delivered from an outlet opening having a diameter greater than that of the first outlet opening.
The combined spray formation has an associated axis and, preferably, the angle between the axis of the first outlet opening and the axis of the combined spray formation has a value falling within the range +7.5xc2x0 to xe2x88x927.5xc2x0. The angle between the axis of the second outlet opening and the axis of the combined spray formation also preferably has a value falling within the range +7.5xc2x0 to xe2x88x927.5xc2x0. It has been found that by arranging the axes in this way, optimum emission levels and combustion noise levels are achieved over a range of engine speeds and loads.
The first and second openings conveniently open into a bore provided in the nozzle body at axially spaced positions. The means for controlling fuel delivery through the first and second outlet openings may comprise an outer needle slidable within the bore to control fuel delivery through the first opening and an inner needle slidable within a bore formed in the outer needle to control fuel delivery through the second outlet opening. Load transmitting means may be provided to transmit movement of the out needle beyond a predetermined position to the inner needle.
One or more additional pairs of first and second openings may be provided. Further openings, for example aligned with the second opening, may be provided if desired.